Having a new CO2 setup for your tank can be an exciting moment for any aquarist, as it upgrades your tank to be able to do more things with plants.
However, after getting everything set up, you then need to figure out the amount of CO2 you should be injecting into your aquarium.
In general, when adding CO2 to your tank you should aim for a concentration level between 10-15 mg/L.
This will provide adequate levels of CO2 for plant growth.
The amount of plants will have the physical amount of CO2 to vary.
Let’s dive into the amount of CO2 to add to your tank, along with some factors to consider that can alter the amounts, as well as some precautions to take when adding CO2.
How Much CO2 is Enough
When trying to achieve the recommended concentration of 10-15 mg/L, it is important to utilize tools and observations to help determine if you are in the ballpark.
What this concentration level provides is a good balance of CO2 being available for plants to grow, while not interfering too much with water parameters, as well as ensuring that the CO2 doesn’t bring oxygen levels too low, where there could be a danger of suffocating your animals.
Common signs of CO2 not being in high enough concentration are if slow plant growth is noticed.
Too high concentrations can be noticed by animals gasping for breath if high concentrations are left for too long, and pH levels that are lowered.
In both cases with too high or too low concentrations of CO2, accelerated algae growth may be observed.
Too low concentrations can result in the existing plants not being able to utilize the available light which algae can capitalize on, with too high concentrations, the added CO2 resources can result in rapid algae growth.
Factors That Affect How Much CO2 is Required
Several factors will affect the amount of CO2 needed, and possibly require further adjustments in the future.
The main factors are tank size, the amount of plants present, the type of plants present, and the amount of light the tank receives.
Tank Size
The tank size is pretty straightforward, as the less amount of water in the tank, the quicker the concentration of CO2 is present with fewer amounts of CO2 being added.
A tank of a larger size will require more CO2 to be pumped in to reach the same concentration levels that a smaller tank will reach with less additional CO2.
Plants
The factor that plants introduce on the other hand is more nuanced, as it greatly depends on the amount and the type.
More plants will require higher concentrations of CO2 to have the plants receive the maximum amount of benefits given by the additional CO2.
Like any other resource, the more items needing that resource require more of that resource.
The type of plants will also impact the amount, as faster-growing plants, many of which will be used in the background, can use more CO2 at quicker rates, than plants that grow at a slower rate.
When considering the amount of CO2 to add, be sure to know the type of plants present in your tank, and don’t be afraid to experiment while monitoring the concentrations to find the perfect balance for your needs.
Lighting
As part of the photosynthesis process, plants require light to use the CO2 as a beneficial resource to help grow.
Without the light, added CO2 will simply dissipate from the water over time without being used by your plants.
With that being said, CO2 will be required in higher amounts if light is being received for longer periods, as it increases the amount of time the plants can utilize it.
Tanks with less amount of light will decrease the necessary amounts of CO2 needed.
To learn about when and how long you should be adding CO2 to your tank, read my article here.
How to Measure and Monitor CO2 Levels In the Tank
Two main key tools are used to help monitor and measure the CO2 levels, this is a bubble counter and a drop checker.
The bubble counter is attached to the CO2 regulator and filled with a liquid, typically water or mineral oil.
Both water and mineral water will perform the same, however, water will require consistent topping off as it evaporates which doesn’t occur with the mineral oil.
This device is used by counting the number of bubbles visibly seen per amount of time which is then used to give an idea of how much CO2 is being added to the tank.
A good starting point for most tanks is roughly one bubble per second.
A drop checker on the other hand measures the concentration of CO2 in your tank.
This tool has a bulb that will hold a special solution that will change colors based on the concentration levels.
There are normally three levels shown by the solution which denote if the CO2 concentration levels are too low, in the range, or too high.
If your drop checker is showing the concentration as being too low then consider increasing the amount of CO2 being added, if too high then lower the CO2 being added, which means increasing the number of bubbles in your bubble counter or decreasing them.
Also remember that the addition of additional plants may change the needs of your tank, and could require further adjustments.
The Role of CO2 in Aquariums
Knowing the right amounts of CO2 you should be using, you may be wondering what role CO2 plays in the ecosystem of a tank.
CO2 is one of the main components in the photosynthesis process for plants.
Plants convert light, water, and CO2 into oxygen and energy.
The energy is then used in the growth and development of the plants, and the oxygen is released into the water, helping to keep your water well-oxygenated for the plants and animals to use for breathing.
Safety Considerations and Possible Impact on Fish
Because there will be some CO2 naturally dissolved into the tank from animal respiration and gas exchange from the surface, there isn’t much danger in having too little CO2 added to a tank.
You may notice slower plant growth if there is too little CO2 in the tank.
The bigger danger is in the instances where too much CO2 is being added to a tank, and the overall oxygen levels of the tank are not enough to combat it.
A common cause for this situation is a malfunction in the filtration unit or air pumps where the surface agitation becomes limited to non-existent, and oxygen is no longer being pumped in.
At this point even if your CO2 levels were appropriate for the tank, the CO2 will begin to cause respiratory issues for the animals.
A big symptom of this case is if you notice fish gasping at the water’s surface as they try to pull oxygen from the air.
You may also notice high-level color being shown in your drop checker as mentioned above.
If either of these situations are noticed, first check that the air pumps, or other equipment being used for surface agitation is functioning, then check if your CO2 is being added at a higher rate than normal.
While performing these tasks, it would be advisable to try to take your animals out of the tank, and into a temporary holding tank, or a bucket with fresh water to begin raising their available oxygen levels.
Excess CO2 levels will also affect your tank’s pH, making it more acidic. As the CO2 is dissolved into the water, H2CO3 or carbonic acid will begin to form. As the carbonic acid concentration increases, the pH will lower, if the additional CO2 is shut off, this concentration will begin to reduce and the pH levels will begin to rise.
Final Thoughts
Adding CO2 is the next step in a planted tank’s evolution, and finding the right balance of CO2 to add is vital in establishing a strong, and robust ecosystem.
Constant monitoring and adjustments are what become key in making a tank thrive and get all available benefits from the additional CO2.